This invention relates to a polyethylene terephthalate multi-layer preform used for plastic blow molding and to a method for making the preform.
Plastic blow molding is conventionally performed by providing a hot plastic parison either from extruded plastic or as a preform which is usually injection molded from plastic. Usually, such preforms are composed of a single type of plastic that is injected into a mold through a single port. However, there have also been attempts to provide coinjection of more than one plastic into a mold so as to provide different layers of plastic.
U.S. Pat. No. 3,878,282 to Bonis et al. discloses a process for molding multi-layer articles that are specifically disclosed as a preform-type parison with different layers. The process involved is performed by injection molding the different layers within different molds while mounted on the same inner mandrel during the injection of each layer.
U.S. Pat. No. 4,307,137 to Ota et al. discloses a method for forming an optical design pattern in polyethylene terephthalate articles which are specifically disclosed as a blow molding preform having inner and outer members with the inner member having an open end defining a thread closure and with the outer member having a junction with the inner member toward a closed end of the preform from the thread closure.
U.S. Pat. No. 4,391,861 to Nilsson discloses a preform of a thermoplastic and has a two-part interfitted construction and at least one intermediate layer that functions as a gas barrier, and also discloses that the outer part may be previously used and reprocessed material.
U.S. Pat. No. 4,646,925 to Nohara discloses a multi-layer preform for draw-blow forming a bottle which has inner and outer layers with a junction that is located toward a closed end of the preform from a closure thread at an open end of the preform. The preform also includes a gas barrier intermediate the inner and outer layers.
U.S. Pat. No. 5,102,705 discloses a bottle made of polyethylene naphthalate resin produced by highly stretching a preform in a manner that is disclosed as limiting gas permeability and x-ray transmission.
There have been attempts in the past such as disclosed by the aforementioned Nilsson patent to utilize post consumer recycled plastic for plastic blow molding since such reuse reduces the need for additional land fills as well as conserving on natural resources in the manufacturing of new articles. Such prior attempts have utilized injection molding or extrusion which necessarily limits the amount of post consumer recycled plastic which can be utilized since it is difficult to injection mold or extrude relatively thin wall preforms or extruded parisons used for plastic blow molding. The maximum amount of post consumer recycled plastic which has been used to date is about 50% by weight of the total weight of the preform.
Blow molding has also previously been performed utilizing a preform that is initially thermoformed from film, i.e. sheet plastic, that provides a moisture and/or oxygen barrier prior to injection molding of an outer protective layer. After the thermoforming, the formed film is trimmed and the outer layer is then injection molded around the thermoformed plastic prior to the finished preform being blow molded to provide the resultant container.
One object of the present invention is to provide an improved polyethylene terephthalate multilayer preform used for plastic blow molding.
In carrying out the above object, the polyethylene terephthalate multi-layer preform used for plastic blow molding has a thermoformed inner layer of virgin polyethylene terephthalate that has a surface defining a hollow interior of the preform. The preform also has an injection molded outer layer of post consumer recycled polyethylene terephthalate that by weight is greater than 75% of the total weight of the preform and the preform has an outwardly exposed exterior surface defined entirely by the outer layer of the post consumer recycled polyethylene terephthalate.
In the preferred construction of the polyethylene terephthalate multi-layer preform, the post consumer recycled polyethylene terephthalate is by weight greater than about 85% of the total weight of the preform, most preferably in the range of about 88-92% of the total weight of the preform, and optimally about 90% of the total weight of the preform.
In the preferred construction, the polyethylene terephthalate multi-layer preform has the inner layer of virgin polyethylene terephthalate thermoformed which permits the relatively thin wall construction thereof that allows the increased use of the greater amount of post consumer recycled polyethylene terephthalate than has been possible in the past.
Another object of the invention is to provide an improved method for making a polyethylene terephthalate multi-layer preform used for plastic blow molding.
In carrying out the immediately preceding above object, the method for making a polyethylene terephthalate multi-layer preform used for plastic blow molding is performed by thermoforming a sheet of virgin polyethylene terephthalate to provide an inner layer and then injection molding an outer layer of post consumer recycled polyethylene terephthalate around the inner layer of virgin polyethylene terephthalate.
In the preferred practice of the method, the thermoforming and injection molding are performed so that the injection molded outer layer of post consumer recycled polyethylene terephthalate is greater than 75% of the total weight of the preform, more preferably greater than about 85% of the total weight of the preform, most preferably in the range of about 88-92% of the total weight of the preform, and optimally about 90% of the total weight of the preform.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.